1	Spiracles present on meso- and metanota (Eosentomata, Eosentomon)	2
–	Spiracles absent (Acerentomata)	9
2	Head setae aa and ap present, notal setae P2a and P3a of equal length (Eosentomon delicatum-group)	3
–	Head setae aa absent, ap present, notal seta P2a shorter than P3a (Eosentomon transitorium-group)	5
3	Foretarsal sensillum c' on the line α6-δ5	Eosentomon carpaticum
–	Foretarsal sensillum c' proximal to the line α6-δ5	4
4	Sensillum c' broadened, P1a on tergite VIII without basal dilation, notal seta P2a longer than P3a	Eosentomon stachi
–	Sensillum c' slender, P1a on tergite VIII with basal dilation, notal seta P2a the same length as P3a	Eosentomon armatum
5	Seta P1a on tergite VII at the same level as P2	6
–	Seta P1a on tergite VII posterior to level of P2	7
6	Seta D2 on metatarsus slender	Eosentomon transitorium
–	Seta D2 on metatarsus spine-like	Eosentomon enigmaticum
7	Sternites IX–X with 6 setae	Eosentomon pinetorum
–	Sternites IX–X with 4 setae	8
8	Seta P1a on tergites II–IV longer than P1, foretarsal sensillum t3 longer than c'	Eosentomon semiarmatum
–	Seta P1a on tergites II–IV shorter than P1, foretarsal sensillum t3 same length as c'	Eosentomon silvaticum
9	Abdominal appendages I–II two-segmented	10
–	Abdominal appendage I two-segmented, appendage II not segmented (Acerentomidae)	12
10	Tergites II–VII with 4 pairs of A-setae, calyx of maxillary gland small	Ionescuellum carpaticum (Hesperentomidae)
–	Tergites II–VII with at most 2 pairs of A-setae, calyx of maxillary gland enlarged (Protentomidae)	11
11	Tergites II–VI with one pair of A-setae, foretarsal sensillum b about 2/3 length of c	Proturentomon minimum
–	Tergites II–VI with 2 pairs of A-setae, foretarsal sensillum b nearly as long as c	Proturentomon sp.
12	Meso- and metanota with 2 pairs of A-setae, abd. appendages II–III each with 3 setae…14	Acerentulus
–	Meso- and metanota with 3 or 4 pairs of A-setae, abd. appendages II–III each with 2 setae	13
13	Meso- and metanota both with 3 pairs of A-setae, foretarsal sensillum t1 filiform, calyx of maxillary gland with racemose appendices	Acerella muscorum
–	Mesonotum with 3 pairs of A-setae, metanotum with 4 pairs of A-setae, sensillum t1 claviform, calyx of maxillary gland smooth (Acerentomon)	21
14	Sternite XI with 4 setae	15
–	Sternite XI with 6 setae	16
15	Foretarsal sensillum b very long, nearly reaching the base of claw, tergite VII with seta P3a	Acerentulus traegardhi
–	Foretarsal sensillum b shorter, nearly equal to length of sensillum c, tergite VII without seta P3a	Acerentulus halae
16	Foretarsal sensillum a short, passing the base of sensillum t2 (Acerentulus cunhai-group)	Acerentulus sp.
–	Foretarsal sensillum a long, nearly reaching or surpassing the base of seta γ3 (Acerentulus confinis-group)	17
17	Tergite VII with 3 pairs of A-setae	18
–	Tergite VII with 4 pairs of A-setae	19
18	Tergite VII with seta P3a, sternite VII with seta Pc	Acerentulus xerophilus
–	Tergite VII without seta P3a, sternite VII without seta Pc	Acerentulus exiguus
19	Tergite VII with seta P3a	20
–	Tergite VII without seta P3a	Acerentulus cf. confinis
20	Maxillary sensilla spindle-shaped, foretarsal sensillum a' slender, sternites II-III without pores	Acerentulus confinis
–	Maxillary sensilla parallel-sided and slender, foretarsal sensillum a' thickened, sternites II-III with pores	Acerentulus alni
21	Tergite VII with pair of x-setae(Acerentulus doderoi-group)	Acerentomon rostratum
–	Tergite VII without x-setae	22
22	Sternite VIII with a pair of posterior setae (Acerentomon affine-group) Acerentomon affine
–	Sternite VIII without posterior setae (23)	Acerentomon microrhinus- group
23	Labrum slightly protruded (LR = 9), foretarsal sensilla a, b and c of the same length	Acerentomon microrhinus
–	Labrum clearly protruded (LR = 7 or less), sensilla a, b and c of unequal lengths	24
24	Foretarsal sensillum b broadened	25
–	Foretarsal sensillum b slender	26
25	Foretarsal sensillum a long, reaching the base of seta γ3, maxillary sensilla spindle-shaped, labial sensillum slender	Acerentomon quercinum
–	Foretarsal sensillum a short, slightly surpassing the base of seta γ2, maxillary sensilla parallel-sided, labial sensillum broadened	Acerentomon cf. quercinum
26	Foretarsal sensillum a longer than c, sternite VI with 5 A-setae	Acerentomon carpaticum
–	Foretarsal sensillum a shorter than c, sternite VI with 7 A-setae	Acerentomon mesorhinus